The invention relates to domestic appliances comprising a catalytic composition for the purpose of deodorizing and oxidizing organic components or carbon.
An object of the present invention is to provide catalytic compositions for domestic appliances which are capable of reducing or eliminating environmental odour pollution (deodorizing) and which are able to oxidize organic components or carbon.
This objective is surprisingly achieved by means of domestic appliances having a catalytic composition which comprises a coating of a coating material on a support and is obtainable by applying the coating material, comprising (1) a polycondensate of
(A) one or more silanes of the general formula (I)
Raxe2x80x94Sixe2x80x94X(4-a)xe2x80x83xe2x80x83(I)
in which the radicals R are identical or different and are non-hydrolysable groups, the radicals X are identical or different and are hydrolysable groups or hydroxyl groups and a has the value 0, 1, 2 or 3, with a being greater than 0 for at least 50 mol % of the silanes, or an oligomer derived therefrom,
(B) if desired, one or more compounds of glass-forming elements, and (2) particles of one or more transition metal oxides, the weight ratio of transition metal oxide particles to polycondensate being from 10:1 to 1:10, to the support and subjecting the applied coating material to thermal treatment, said catalytic composition representing a component of said domestic appliance or of a device connected with said domestic appliance.
In the hydrolysable silanes (A), the hydrolysable groups X are, for example, hydrogen or halogen (F, Cl, Br or I), alkoxy (preferably C1-6 alkoxy, such as methoxy, ethoxy, n-propoxy, i-propoxy and butoxy), aryloxy (preferably C6-10 aryloxy, such as phenoxy), acyloxy (preferably C1-6 acyloxy, such as acetoxy or propionyloxy), alkylcarbonyl (preferably C2-7 alkylcarbonyl, such as acetyl), amino, monoalkylamino or dialkylamino having preferably from 1 to 12, in particular from 1 to 6, carbon atoms.
The non-hydrolysable radicals R may be non-hydrolysable radicals R1 or may be radicals R2 which carry a functional group, R1 being preferred.
The non-hydrolysable radical R1 is, for example, alkyl (preferably C1-8 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl and t-butyl, pentyl, hexyl, octyl or cyclohexyl), alkenyl (preferably C2-6 alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (preferably C2-6 alkynyl, such as acetylenyl and propargyl) and aryl (preferably C6-10 aryl, such as phenyl and naphthyl). The stated radicals R1 and X may if desired have one or more customary substituents, such as halogen or alkoxy, for example.
Specific examples of the functional groups of the radical R2 are the epoxy, hydroxyl, ether, amino, monoalkylamino, dialkylamino, amide, carboxyl, vinyl, acryloyloxy, methacryloyloxy, cyano, halogen, aldehyde, alkylcarbonyl, and phosphoric acid group. These functional groups are attached to the silicon atom via alkylene, alkenylene or arylene bridging groups, which may be interrupted by oxygen or xe2x80x94NHxe2x80x94 groups. The stated bridging groups are derived, for example, from the abovementioned alkyl, alkenyl or aryl radicals. The radicals R2 contain preferably from 1 to 18, in particular from 1 to 8, carbon atoms.
In one preferred embodiment, the silanes (A) comprise a mixture of
(A1) at least one hydrolysable silane of the general formula (II)
SiX4xe2x80x83xe2x80x83(II)
in which the radicals X are identical or different and are hydrolysable groups or hydroxyl groups, or an oligomer derived therefrom, and
(A2) at least one organosilane of the general formula (III),
R1a1R2a2SiX(4-a1-a2)xe2x80x83xe2x80x83(III)
in which R1 is identical or different at each occurrence and is a non-hydrolysable group, R2 is identical or different at each occurrence and is a radical which carries a functional group, X has the above definition and a1 and a2 have the value 0, 1, 2 or 3, the sum (a1+a2) having the value 1, 2 or 3, or an oligomer derived therefrom in a molar ratio (A1):(A2) of 5-50:50-95.
In the general formula (III), a1 preferably has the value 1 or 2, a2 preferably has the value 0, 1 or 2 and the sum (a1+a2) preferably has the value 1 or 2.
Particularly preferred hydrolysable silanes (A) and (A1) are tetraalkoxysilanes such as tetraethoxysilane (TEOS). Particularly preferred hydrolysable silanes (A) and (A2) are alkyltrialkoxysilanes, preferably containing C1-C8 alkyl, especially methyltriethoxysilane, aryltrialkoxysilanes, especially phenyltriethoxysilane, dialkyldialkoxysilanes, preferably containing C1-C8 alkyl, especially dimethyldiethoxysilane, and diaryldialkoxysilanes, especially diphenyldiethoxysilane. Silanes containing functional groups (A) and (A2) are, for example, epoxy silanes such as 3-glycidyloxypropyltrimethoxysilane (GPTS) and amino silanes such as 3-aminopropyltriethoxysilane and 3-(aminoethylamino)propyltriethoxysilane (DIAMO).
In the silane component (A) according to formula (I), a is greater than 0 for at least 50 mol % of the silanes, i.e. at least 50 mol % of the silanes contain at least one non-hydrolysable group R. The silane component (A) preferably comprises from 50 to 95 mol % of silanes having at least one non-hydrolysable group R. With regard to the formulae (II) and (III), the preferred molar ratio of the hydrolysable silane (A1) to the organosilane (A2) in the polycondensate is 5 to 50:50 to 95, preferably from 1:1 to 1:6 and with particular preference from 1:3 to 1:5. A particularly favourable molar ratio is 1:4.
The optional component (B) constitutes glass-forming elements which are preferably dispersible or soluble in the reaction medium. It is possible to use, for example, compounds (halides, alkoxides, carboxylates, chelates, etc.) of lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium, barium, boron, aluminium, titanium, zirconium, tin, zinc or vanadium.
To prepare the polycondensate (1), the starting components (A) and, where appropriate, (B) are hydrolysed and condensed. The hydrolysis and condensation are conducted either in the absence of a solvent or, preferably, in an aqueous or aqueous/organic reaction medium, where appropriate in the presence of an acidic or basic condensation catalyst such as HCl, HNO3 or NH3. The hydrolysis and condensation preferably take place in the presence of an aqueous acid. The aqueous acids are used preferably in a concentration range of from 0.1 N to 10.0 N. Acids used with preference are hydrochloric, nitric, phosphoric and acetic acid.
Additionally, during the preparation of the polycondensate, the inorganic particles set out below may be added. During the preparation, preferably, nanoscale inorganic particles, especially in the form of a sol, are added. By way of example, silica sols may act as hydrolytically active compounds in the sol. Suitable for this purpose are commercially customary silica sols, such as the Levasils(copyright), silica sols from Bayer AG, for example.
When a liquid reaction medium is used, the starting components are soluble in the reaction medium. Particularly suitable organic solvents are water-miscible solvents, such as monohydric or polyhydric aliphatic alcohols, for example, but also aliphatic or aromatic hydrocarbons, such as those having from 5 to 20 carbon atoms, ethers, esters, ketones, amides and alkylamides.
The hydrolysis and polycondensation preferably take place under the conditions of the sol-gel process, the reaction mixture being used in the viscous sol state to coat the substrate.
Where appropriate, the hydrolysis and polycondensation are carried out in the presence of a complexing agent, examples of such agents being nitrates, xcex2-dicarbonyl compounds (e.g. acetylacetonates or acetoacetates), carboxylic acids (e.g. methacrylic acid) or carboxylates (e.g. acetate, citrate or glycolate), betaines, diols, diamines (e.g. DIAMO) or crown ethers.
The ratio of the hydrolytically active components to the hydrolysable silanes (and, where appropriate, to the glass-forming elements) may be characterized by the value ROR. The ROR value represents the molar ratio of water from the hydrolytically active components (water, aqueous acid, silica sol, etc.) to the abovementioned hydrolysable groups X from the silane components (and, where appropriate, the corresponding hydrolysable groups of the glass-forming elements). The sol obtained possesses, for example, an ROR value of from 0.1 to 10 and preferably from 0.2 to 2.
The polycondensate obtained is mixed, preferably in the form of a sol, with particles of one or more transition metal oxides, the ratio of transition metal oxide particles to polycondensate being from 10:1 to 1:10, preferably from 10:1 to 1:1 and with particular preference from 10:1 to 2:1. In the case of this ratio, account is taken for the polycondensate, with the exception of any other organic solvent, of the components added for the purpose of preparing the polycondensate (in particular the inorganic particles for preparing the condensate).
The average particle diameter of the transition metal oxides used is situated, for example, in a range from 10 nm to 20 xcexcm. In the case of coated substrates which are to be used for improving odour, it is preferred to use transition metal oxide particles having an average particle diameter of from 1 to 20 xcexcm.
The particles consist substantially, or preferably completely, of transition metal oxide. The transition metal oxide particles may be composed of one transition metal oxide or of transition metal oxide mixtures. In the case of the transition metal oxide mixtures, which are used with preference, it is preferred to combine different transition metal oxide powders with one another so as to give particles comprising different transition metal oxides. It is of course also possible to use particles which contain different transition metal oxides.
In the case of use for oxidation purposes in particular, however, it is possible, besides the particles consisting essentially of transition metal oxides, to make additional use, in whole or in part, of particles which have the transition metal oxides indicated below at the surface but which otherwise are composed of a different material. In that case the transition metal oxide particles are composed of particles of a material chosen preferably from one of the materials specified below for the inorganic particles, said material being surface-coated with one or more transition metal oxides. Preferably, these particles are coated fully on the surface with the transition metal oxides. For the weight ratio of transition metal oxide particles to polycondensate, these particles are taken into account as a whole as transition metal oxide particles. The particles in question are in particular the particles in the micrometre range, indicated below, which have been provided on the surface, and/or impregnated, with transition metal oxides.
The transition metal oxides in question are, in particular, catalytically active transition metal oxides which have deodorizing and/or oxidizing properties. By transition metals are meant, as is customary, the elements of transition groups I to VIII of the Periodic Table and the lanthanide and actinide elements. With particular preference the transition metal oxide is selected from the oxides of the metals La, Ce, Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag and Zn or from mixtures of these metal oxides. Preference is given to using transition metal oxide mixtures, with mixtures of the oxides of Mn and Ce with one or two further transition metals, such as mixtures of the oxides of Mn/Co/Ce, Mn/Cu/Ce, Mn/Ni/Ce, Mn/Fe/Ce or Mn/Co/Ni/Ce, being particularly preferred. A further-preferred transition metal oxide mixture is a mixture of the oxides of Cu/V/La. It is also possible to use mixed oxides of the aforementioned transition metals.
In the transition metal oxide mixtures, the following amounts of the corresponding metal oxides in the metal oxide mixture are preferred: Ce: 1-70% by weight, V: 5-70% by weight, Mn: 20-95% by weight, Fe: 20-95% by weight, Co: 1-50% by weight, Ni: 1-50% by weight, Cu: 1-95% by weight.
Specific examples of transition metal oxides are MnO2 (pyrolusite), xcex3-MnO2, Co3O4, CO2O3, COO and CeO2. It is of course also possible to use any other suitable transition metal oxide.
The BET surface area of the particles used is situated, for example, within a range from 1 to 100 m2/g.
Besides the transition metal oxide particles, cocatalysts may also be used in the coating material, in amounts for example of from 1 to 5% by weight, based on the transition metal oxide particles. Suitable cocatalysts are, for instance, K, Mg, Ca, Ba and Sr salts and also Al oxide and Sn oxide. Examples of suitable salts are the corresponding halides, hydroxides, nitrates, carbonates, or phosphates. They may be added, for example, by mixing the cocatalyst with the transition metal oxide particles or with the mixtures of the transition metal oxide particles prior to addition to the polycondensate, or by separate addition of the cocatalyst to the coating material. In the former case, it is preferred to use powders, and in the latter case it is preferred to use readily soluble salts of the cocatalyst.
The coating material may also include inorganic particles, which may be added during the preparation of the polycondensate or of the coating material or thereafter. These particles may be nanoscale inorganic particles or particles in the micrometre range. It is also possible to add particles of both orders of magnitude, in which case the particles in the micrometre range are employed in particular when the catalytic composition is used for oxidizing organic components or carbon.
The inorganic particles may be composed of any desired materials, with oxides being preferred. Preferred oxides are oxides of Si and Al (especially boehmite). The particles may be added, for example, in the form of powders or, especially the nanoscale particles, in the form of sols.
The nanoscale inorganic particles preferably possess an average particle size of up to 300 nm, in particular up to 100 nm and with particular preference up to 50 nm. The particles may be added in colloidal form. In this case they can comprise sols or dispersible powders. Specific examples of nanoscale inorganic particles are SiO2, Al2O3, SnO2, iron oxides or carbon (carbon black and graphite), especially SiO2. Very particular preference is given to using silica sols as nanoscale inorganic particles.
Especially if the catalytic compositions are to be used as oxidative compositions, inorganic particles in the micrometre range may also be added to the coating material. They serve to structure the coating and to produce cavities. These particles possess an average particle diameter of, for example, from 1 to 500 xcexcm, preferably from 10 to 300 xcexcm. They are preferably oxide- and/or hydroxyl-containing compounds of the elements from main groups III and IV, such as aluminium oxides or silicon oxides. They may have been activated. Examples that may be mentioned include kieselguhr, alumina 90, silica gel 40 or silica gel 60, produced by the company Merck.
Prior to their use, the abovementioned inorganic particles in the micrometre range may be impregnated with metal salts or mixtures of metal salts, such as chlorides, phosphates, formates, nitrates or acetates, and then treated at elevated temperatures in order to generate catalytically active metal oxides on the surface. Preference is given to using metal nitrates or metal acetates, since the anions form volatile products when treated within the temperature range used. Metals used are the transition metals specified for the transition metal oxide particles. In this case particles are obtained which are provided on the surface with transition metal oxides, which are used in accordance with the invention as transition metal oxide particles, and which are taken into account as a whole for the weight ratio of transition metal oxide particles to polycondensate.
The coating material may also comprise further additives. It is possible, for example, to use additives suitable for adjusting viscosity and/or, in particular, for generating cavities during the thermal treatment of the coating materials. For this purpose it is possible, for example, to use customary thickeners. Specific examples are cellulose derivatives, such as hydroxypropylcellulose, starch, modified starch, polyvinyl alcohol and glycols, e.g. polyethylene glycol. Preference is given to using cellulose derivatives, especially hydroxypropylcellulose. In addition it is also possible to use the additives customary in catalytic compositions, such as pigments (e.g. black pigments).
The viscosity of the sol mixed with the transition metal oxide particles may also be adjusted, if desired, by removing or adding a solvent, e.g. one of those mentioned above. In this form, the sol is usually also storable for long periods. Where appropriate, it may be activated by adding water or aqueous acid, in which case the coating material is preferably used within one month.
The coating material is applied to the support by customary coating methods. Applicable techniques are, for example, dipping, flow coating, spin coating, spraying or brushing.
Suitable supports are, for example, those of metals such as stainless steel, steel, copper, brass and aluminium; metal oxides, glasses such as float glass, borosilicate glass, lead crystal or silica glass; glass ceramics, and ceramics such as Al2O3, ZrO2, SiO2 mixed oxides, or else enamel, but also porous supports such as porous ceramics, for example. The shape of the supports is arbitrary. The supports in question may be planar or structured. Particularly suitable supports are those in the form of meshes, honeycombs or nets, such as wire meshes, examples being steel wire meshes, ceramic honeycombs or wire nets.
The supports may be pretreated prior to the application of the coating material. For example, they are subjected to cleaning, using commercially customary alkaline cleaners, for example. It is likewise possible, for example, by heat-treating steel supports and forming chromium oxide whiskers on the surface, to bring about substantially improved adhesion of the coating material to steel supports.
The resulting coating is subjected to initial drying, if desired, and then heat-treated. This can be done at temperatures of from 200xc2x0 C. to 700xc2x0 C., preferably from 300xc2x0 C. to 400xc2x0 C. The heat treatment may be carried out in air on in an inert gas such as nitrogen or argon. The heat treatment may also take place if desired by means of IR or laser radiation. The heat treatment may be accompanied, for example, by drying, curing or consolidation or compaction of the coating material.
The coating operation is preferably performed so as to give coat thicknesses of from 0.01 to 500 xcexcm, preferably from 1 to 500 xcexcm. Where the catalytic compositions are used for the purpose of deodorizing, coat thicknesses of from 30 to 100 xcexcm, in particular from 25 to 75 xcexcm, are preferred. Where the catalytic compositions are used as oxidatively active surfaces, coat thicknesses of from 1 to 10 xcexcm are suitable when using transition metal oxides having an average particle size of less than 200 nm. The catalytic compositions which serve as oxidatively active surfaces, and which additionally comprise inorganic particles in the micrometre range, preferably have coat thicknesses of from 100 to 400 xcexcm.
The catalytic compositions of the invention may have a porous or a non-porous coating. Preferably, the catalytic compositions have porous coatings. The pores may comprise microscopically visible cavities on the surface and/or relatively fine micropores. The cavities visible on the surface under the microscope have an approximately globular morphology (hemispheres) and their diameter is from about 1 to 5 xcexcm. Their extent and form in the interior of the coat cannot be determined by microscopy. The determination of the BET surface areas of preferred embodiments indicates that relatively fine micropores are present therein alternatively or additionally.
The catalytic composition of the invention has a deodorizing effect; in other words, odour pollution caused by substances can be reduced or avoided completely. The deodorizing activity is found in particular at temperatures above 150xc2x0 C., for example at temperatures from 150 to 500xc2x0 C., preferably from 200 to 350xc2x0 C. The odour-polluted air is guided past the catalytic composition at elevated temperatures. As it passes, substances present in the air are degraded.
The catalytic composition is also capable of oxidizing organic components or carbon, such as carbon black or graphite, which are present, for example, on the surface of the catalytic composition. The oxidizing activity is found in particular at the temperature ranges indicated above.
The catalytic compositions are preferably used for these purposes in such a way that they are located directly on any surface of the domestic appliance in question, in which case this surface acts as the substrate, or they represent a component of an additional device, connected where necessary via a connecting line, within or in the vicinity of the domestic appliance. The surface of the domestic appliance may, for instance, be part of the casing or an inner wall, preferably formed of metal. The additional device may, for instance, be an exhaust means of the domestic appliance. In addition to the catalytic composition, the additional device may e.g. comprise heating and venting means.
In this manner, the invention provides a simple way to combat malodors or surface staining which may occur in households and domestic appliances. Domestic appliances in accordance with the present invention are all articles and devices normally used in households. Suitable examples are stoves, stove-tops, kitchen vents and deep-fat fryers. Preferred field of application are electrical and gas stoves, kitchen vents and/or deep-fat fryers.